I've been wondering who people would have as their top 3 sweet girls gone psycho. Meaning, they start out sweet and innocent at the start of the show, but somewhere down the road (middle or ending) they show their true colors and turn into psychopaths. Please give a description as to why you picked them and if possible a picture as well. Please put the pictures as spoilers.
Here are mine:

1. Minatsuki Takami a.k.a "Hummingbird" from Deadman Wonderland

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The first time I saw her, I thought she was a very interesting character and that she would maybe bring something into the show. Boy, was I right. This so-called sweet and shy girl that has flowers decorating her room turned into a psychopath when she went into the Carnival Corpse with Ganta. According to her, she get sexually aroused by seeing others suffer. Frightening...

2. Sekai Saionji from School Days

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Do I really need an explanation for her?? She started out ok for me but towards the middle and most certainly at the end, she went psycho wanting Makoto to be with her and no one else. That's why she had to do what she did.

Another one I'm really not sure I need an explanation for. She started out WAY better for me and it really pissed me off that Makoto did what he did to her. But she didn't have to go down a psycho path and do what she did, still wanting to be with him. And she really didn't need to do what she did at the very end.

For the sake of the thread containing more than a handful of characters, I am going to adopt a VERY liberal definition of Psychopath.

1. Priscilla -- Claymore

2. Sayaka -- Madoka Magica

3. Pirako -- Gintama

Edit: I just noticed OP asked for our reasons in picking them, so here goes:
1.Priscilla -- One of those situations where just being a kid can be destructive in itself. She had such a strong notion of justice, but when that notion is questioned, she is just unable to fathom any other ideas. I don't want to spoil anything, but that moment when she loses control, and you can see the despair in her face... Best part of the show.
2.Sayaka -- Can't say much without pretty big spoilers, but if you've seen the picture that I posted before, then you probably know that that scene was one of the most dramatic moments of the show, and depicted quite well what it means to lose your mind.
3.Pirako -- One among many anime girls that can make cuteness kinda scary. Of those girls, she wins out in my book.